Electron beam plasma amplifier with a wave-guide coupling



Sept. 20, 1966 K. R. u. WEIMER ETAL 3,274,507

ELECTRON BEAM PLASMA AMPLIFIER WITH A WAVE-GUIDE COUPLING Filed Jan. 8, 1962 INVENTOR V kart Ruwelmer Marinus T. Vlaardmgerbroek United States Patent 3,274,507 ELECTRON BEAM PLASMA AMPLIFIER WITH A WAVE-GUIDE COUPLING Karl Richard Ulrich Weimer and Marinas Tennis Vlaardingerbroek, Emrnasingel, Eindhoven, Netherlands, assignors to North American Philips Company, Inc., New York, N.Y., a corporation of Delaware Filed Jan. 8, 1962, Ser. No. 164,762 Claims priority, application Netherlands, Jan. 13, 1961, 260,047 3 Claims. (Cl. 330-41) The invention relates to a sign-a1 amplifying device comprising an electron beam tube, in which the signal to be amplified is fed to an input coupler and the amplified signal is derived from an output coupler, farther remote from the electron gun and in which the signal is amplified by the interaction of the electron beam with a plasma having a plasma frequency which is at least equal to the signal frequency. Such a device is described in Physical Review, vol. 109, No. 4, pages 1393-1394 (1958). In this case the electron beam is modulated with the aid of a short helix with the signal to be amplified and then guided along the axis of the positive column of a mercury vapour discharge. Beyond the interaction space of plasma and beam the electron beam is coupled by means of "a second helix with an output coupler, so that an amplified signal is obtained.

With the known device a modulated beam is guided across the plasma whereas input and output coupling take place beyond the interaction space of the electron beam and the plasma on the beam. The electron beam is modulated in the conventional manner with the signal, in the manner described in the said device, for example with the aid of helices. In order to obtain the desired couplings these helices may sometimes require great dimensions. When using high frequency signals, for example of more than 10,000 mc./s. there is the disadvantage that the couplers can be constructed only with difiiculty. Moreover, to each frequency it applies that the length of the electron beam, owing to the couplers, must be considerably greater than the interaction space of the beam and the plasma.

The invention obviates these disadvantages by providing a particular embodiment of the couplers. It is based on the recognition of the fact that within the interaction space of the beam and the plasma provision is made not only of a modulated beam and a plasma, but also of a modulated beam and a modulated plasma. It is hence possible to carry out the coupling operation in the plasma space. This means that, if by some means the plasma is set oscillating the device can also provide an amplification of the signal.

In accordance with the invention at least one of the signal couplers is located in the range of the plasma while the coupler is constructed in the form of a coupler suitable for use in a waveguide system. This arrangement has the advantage that coupling can be obtained in a simple manner, since it is not bound to the shape characteristic of an electron beam, while the length may be shorter. The construction in the form of a coupler suit-able for use with a waveguide system may be obtained by means of a loop, a coupling hole or an antenna.

At least one of the signal couplers is particularly located in the interaction range of the electron beam and the plasma since this provides an improved signal transfer.

The invention furthermore relates to an electron beam tube comprising a coupler for supplying the signal to be amplified, an output coupler farther remote from the electron gun for deriving the amplified signal and means for producing a plasma by the interaction of which with the electron beam signal amplification is obtained, in

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which at least one of the signal couplers is located in the range of the plasma while the coupler is constructed in the form of a coupler suitable for use in a waveguide system. At least one of the signal couplers is located particularly in the interaction space of the electron beam and the plasma.

The electron beam is produced in the conventional manner by an electron gun and an anode located behind the former, while the beam may strike a collector at the end of the tube. In the device according to the invention a collector may be dispensed with, since the beam may terminate owing to collisions of beam electrons with the plasma particles. Since in accordance with the invention the coupling is performed with the plasma the output coupler may be arranged beyond the interaction space of the beam and the plasma. A plasma is to be understood to denote herein a mixture of positively and negatively charged particles, which can be produced between a cathode, which may be a heating cathode, and an anode. The electrons in the plasma perform an oscillatory motion, of which the frequency, the so-called plasma frequency, depends upon the electron density in the plasma.

The invention will now be described more fully with reference to the drawings, in which FIG. 1 shows diagrammaticaly an electron beam tube and FIG. 2 shows diagrammatically a different embodiment of such an electron beam tube.

The electron beam tube shown in a diagrammatical sectional view in FIG. 1 comprises a gun I and an anode 2 for producing the electron beam. This beam anode 2 serves, moreover, as a plasma anode. The plasma is produced between this plasma anode and the plasma cathode 3 in the glass bulb 4. Through the glass wall are taken the input coupler 5 and the output coupler 6. These couplers are shaped in the form of a loop. To the input coupler 5 is fed the signal to be amplified from a device which is not shown, whereas the amplified signal is fed by the output coupler 6 to a further device not shown. The plasma cathode 3, which is shaped in the form of heating cathode, serves moreover as a beam collector.

In a given construction of this tube the plasma is obtained by a mercury vapour discharge at a pressure of 2X l0 torr, a discharge current across the plasma of ma. and a voltage between the plasma cathode and the plasma anode, the so-called burning voltage of the plasma of 20 v. The electron density in the plasma amounts to about 2x 10 cm. This density corresponds to a plasma frequency of about 4000 mc./s. With this adjustment the tube is therefore suitable for amplifying signals having a frequency of not more than 4000 mc./s. with which signal frequency the maximum amplification is obtained. The voltage between the cathode and the anode in the beam is 300 v., whereas the beam current amounts to 2 ma. When the beam enters the interaction space, it has a diameter of 2 mms.

The electron beam tube shown diagrammatically in FIG. 2 comprises a gun 11 and an anode 12 for producing an electron beam. This beam anode 12 serves, moreover, as a plasma cathode. The plasma is produced between this plasma oathode and the plasma anode 13 in the glass bulb 14. The input coupler is shaped in the form of a coupling hole 15 and the output coupler is shaped in the form of an antenna 16. The signal supply device and the signal output device connected herewith are not shown. The plasma anode 13 serves, in addition, as a beam collector, if the beam has not yet been annulled by collision with plasma particles.

What is claimed is:

1. An electron beam plasma amplifier comprising an envelope containing an ionizable gaseous medium, means within said envelope for generating an electron beam, first and second electrodes directly in the path of the electron beam defining a plasma discharge space and for generating a plasma, coupling means for introducing an input signal of given frequency directly into said plasma discharge space, said plasma having a plasma frequency which is at least equal to the signal frequency, the signal being amplified by interaction between the electron beam and the plasma, and output coupling means for extnacting an amplified signal from said plasma discharge space, said output coupling means being positioned more remote from said electron beam generating means than said input coupling means, at least one of said coupling means being a wave-guide coupler and being positioned in the plasma discharge space.

2. An electron beam plasma amplifier comprising an envelope containing an ionizable gaseous medium, an electron gun within said envelope for generating an electron beam, said electron gun comprising a cathode and an apertured anode for the passage of the electron beam, a second cathode spaced from and operatively associated with said anode and defining a plasma discharge space in which plasma is produced from said ionizable medium, coupling means between said anode and said second cathode for introducing an input signal of given frequency into said plasma discharge space, said plasma having a plasma frequency which is at least equal to the signal frequency, the signal being amplified by interaction between the electron beam and the plasma, and output coupling means for extracting an amplified signal from said plasma discharge space, said output coupling means being positioned more remote from said anode than said input coupling means, at least one of said coupling means being a wave-guide coupler and being positioned in the plasma discharge space.

3. An electron beam plasma amplifier comprising an envelope containing an ionizable gaseous medium, an electron gun within said envelope for generating an electron beam, said electron gun comprising a cathode and an apertured anode for the passage of an electron beam, a second cathode spaced from and operatively associated with said anode and defining a plasma discharge space in which plasma is produced from said ionizable medium, coupling means between said anode and said second cathode for introducing an input signal of given frequency into said plasma discharge space, said plasma having a plasma frequency which is at least equal to the signal frequency, the signal being amplified by interaction between the electron beam and the plasma, and output coupling means for extracting an amplified signal from said plasma discharge space, said output coupling means being positioned more remote from said anode than said input coupling means, at least one of said coupling means being a wave-guide coupler and being positioned in the interaction region of the electron beam and the plasma.

References Cited by the Examiner UNITED STATES PATENTS 1,984,499 12/1934 St. Laurent 33041 X 2,750,455 6/1956 Geisler 33041 X 2,806,974 9/1957 Haeff a 315-3.6 2,817,045 12/1957 Goldstein 31539 2,848,649 8/1958 Bryant 31539 3,099,768 7/ 1963 Anderson.

3,111,604 11/1963 Agdur 33041 .JAMES W. LAWRENCE, Primary Examiner.

GEORGE N. WESTBY, DAVID J. GALVIN,

Examiners.

V. LAFRANCHI, S. SCHLOSSER, R. SEGAL,

Assistant Examiners. 

1. AN ELECTRON BEAM PLASMA AMPLIFIER COMPRISING AN ENVELOPE CONTAINING AN IONIZABLE GASEOUS MEDIUM, MEANS WITHIN SAID ENVELOPE FOR GENERATING AN ELECTRON BEAM, FIRST AND SECOND ELECTRODES DIRETLY IN THE PATH OF THE ELECTRON BEAM DEFINING A PLASMA DISCHARGE SPACE AND FOR GENERATING A PLASMA, COUPLING MEANS FOR INTRODUCING AN INPUT SIGNAL OF GIVEN FREQUENCY DIRECTLY INTO SAID PLASMA DISCHARGE SPACE, SAID PLASMA HAVING A PLASMA FREQUENCY WHICH IS AT LEAST EQUAL TO THE SIGNAL FREQUENCY, THE SIGNAL BEING AMPLIFIED BY INTERACTION BETWEEN THE ELECTRON BEAM AND THE PLASMA, AND OUTPUT COUPLING MEANS FOR EXTRACTING AN AMPLIFIED SIGNAL FROM SAID PLASMA DISCHARGE SPACE, SAID OUTPUT COUPLING MEANS BEING POSITIONED MORE REMOTE FROM SAID ELECTRON BEAM GENERATING MEAN THAN SAID INPUT COUPLING MEANS, AT LEAST ONE OF SAID COUPLING MEANS BEING A WAVE-GUIDE COUPLER AND BEING POSITIONED IN THE PLASMA DISCHARGE SPACE. 